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Tutorial Request - Lens Distortion

 
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gordonrobb



Joined: 17 Mar 2005
Posts: 285

PostPosted: Sat Sep 29, 2007 3:15 am    Post subject: Tutorial Request - Lens Distortion Reply with quote

I was wondering if it would be possible to have a tutorial that shows the whole pipeline for working out lens distortion, solving, exporting to 3d app, and using SE to re-distort the CG footage. Don't know how big a ask this is, but thought I would ask anyway.

Thanks.
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PaulF



Joined: 19 Jun 2005
Posts: 49
Location: County Durham, UK

PostPosted: Sat Sep 29, 2007 5:37 am    Post subject: Reply with quote

I'd love to see this as well. Everything from padding the footage to distorting the CG. It's something that I've never been able to get my head around.

Cheers.
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ssontech
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Joined: 16 Mar 2005
Posts: 611
Location: Valley Forge, Pennsylvania

PostPosted: Mon Oct 08, 2007 11:24 am    Post subject: Reply with quote

I agree this is a good idea. It's not something I can crank out instantly, just because the topic is rather lengthy, but I'll see what I can come up with eventually.
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gordonrobb



Joined: 17 Mar 2005
Posts: 285

PostPosted: Mon Oct 08, 2007 11:34 am    Post subject: Reply with quote

Cheers Russ. Looking forward to it.
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Smola Martin



Joined: 02 Aug 2006
Posts: 35
Location: Czech Republic - Liberec

PostPosted: Mon Oct 08, 2007 11:53 am    Post subject: Reply with quote

it´s good tip for tutorial. Before I didn´t think about it. Easy I click automatic calculate and it was all what I did. But now I know it is very important value for tracking.
I did several calibrate shot my camera and now is tracking solve more accurate.
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gordonrobb



Joined: 17 Mar 2005
Posts: 285

PostPosted: Mon Dec 10, 2007 4:22 pm    Post subject: Reply with quote

Any movement on a tutorial for lens distortion russ?
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ssontech
Site Admin


Joined: 16 Mar 2005
Posts: 611
Location: Valley Forge, Pennsylvania

PostPosted: Tue Dec 11, 2007 6:18 pm    Post subject: Reply with quote

I did come across a nice example shot for at least part of this, but I need to see if I can pin down the permissions aspects.

One thing is for sure---I am seeing a lot of people shooting with their shiny 16:9 HD cameras with the lens wide open. Unless you could buy a nice sportscar for the same cost as the lens, you're pretty much guaranteeing trouble. You can do it, but it's going to be a lot more trouble than if you cut the zoom 20% down from its widest setting.
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gordonrobb



Joined: 17 Mar 2005
Posts: 285

PostPosted: Tue Dec 11, 2007 6:21 pm    Post subject: Reply with quote

Ah cool Russ. Hoping to shoot some test stuff myself, and would like to have at least some idea what to do about lens distortion.

Thanks.
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gordonrobb



Joined: 17 Mar 2005
Posts: 285

PostPosted: Wed May 21, 2008 9:12 am    Post subject: Reply with quote

I was wondering if there was any movement on a tutorial on lens distortion. Pretty please Smile
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LFGabel



Joined: 16 Mar 2005
Posts: 298
Location: Vancouver Island, BC, Canada

PostPosted: Thu May 22, 2008 2:03 am    Post subject: This isn't a video tutorial, but maybe it will help Reply with quote

This is Maya-centric. Adjust for your own CG app.

1. Determine the lens distortion in SynthEyes, either with lens lines, or calculation.

2. In image preparation, enter your lens distortion, click "Apply Distortion" and play with the scale until no black edges appear. The reciprocal of this is your camera scale factor in Maya. For example. if your scale ends up being 0.9000, the camera scale in Maya is 1/0.9000, or 1.11. Take note of it.

3. Return your scale back to 1, and unclick "Apply Distortion". Click OK.

4. Track and solve your shot on the UNDISTORTED plate. Export solve to Maya.

5. Change the camera scale factor in Maya (shape tab).

6. Change the render resolution to match the scale factor. THIS IS IMPORTANT. For example, if you determine that your scale factor is 1.11, and you are rendering to 1920x1080, then change your render resolution to (1920 x 1.11) x (1080 x 1.11). In this example it is 2131x1199. You need to do this so when you redistort the CG to match the plate, no curved edges of the CG will show up when they reach the edge of the frame.

7. Render your CG.

8. Load your CG into SynthEyes.

9. In image preparation, enter the distortion coefficient and the scale (not the reciprocal value) you determined in step 2. Click "Apply Distortion". Go to the output tab, output the sequence.

10. We're still not done, since the CG still needs to be scaled down to the source plate's size. Load your distorted CG into your compositing app, and scale down to your source plate resolution. In this example, I resampled to 1920x1080, aspect 1.778, matching the aspect and resolution of the source plate.

You're done. I hope it makes sense.

By the way, this will only work with barrel or pincushion distortion. Hybrid distortion like mustache distortion (combination of barrel and pincushion) is another can of worms that crops up when low quality lenses are used.
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gordonrobb



Joined: 17 Mar 2005
Posts: 285

PostPosted: Thu May 22, 2008 4:08 am    Post subject: Reply with quote

Lee

Let me see if I understand this. (I will look at it in more detail later with LW in front of me)

Are you basically saying.

In SE you undistort the footage, then do the solve, which you export to your 3D package.

In 3D app, you do your CG, create your movie (of the CG element)

Then back in SE you load your CG element, and apply distortion to bring it back in line with the original footage which can then be comp'd in your comp application?
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LFGabel



Joined: 16 Mar 2005
Posts: 298
Location: Vancouver Island, BC, Canada

PostPosted: Thu May 22, 2008 12:12 pm    Post subject: Reply with quote

Yes. This is one way to do it. I prefer to do the final distortion of the CG and compositing all in one pass using Shake.

You can also export undistorted proxy plates if you want to see everything line up in your 3d app.

I'm not sure what the equivalent of camera scale in Lightwave would be. Once you figure that out, please let everyone know.

But remember, you need to render more than you need (thus the camera scale and higher resolution render) because applying distortion introduces the edges of the frame, and if a CG element moved off frame, you'd see the curved edge of the frame.
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